Since the invention of dynamite in 1866, explosive blasting has been the primary technique utilized for the excavation of hard rock. Despite many improvements in rock excavation technology over the years, methods suitable for the continuous excavation of hard rock do not yet exist, whether for mining or civil construction. Conventional drill and blast remains the only technique which may be utilized to excavate the harder rocks, such as granite and gneiss, with reasonable efficiency. Numerous mechanical and water jet assisted systems have been developed for the efficient excavation of softer, typically sedimentary rocks. Recent improvements in tunnel boring machines have allowed these machines to cut relatively hard rock up to 300 MPa in compressive strength, but cutter wear remains a serious problem. These systems are not able to effectively excavate the harder rocks, however. Also the TBM type of machines are limited in their mobility and in their ability to cut irregularly shaped openings.
Conventional drill and blast, while being able to excavate the hardest of rocks at acceptable efficiencies, is limited, in that the technique must be applied in a cyclic drill, blast and muck fashion, resulting in the inefficient and often interfering use of the machines required for each cycle. Conventional drill and blast is also limited, in that considerable damage is done tc the rock left around the structure being excavated, with this residual damage often requiring additional and expensive ground support. For commercial mining operations, the conventional drill and blast method is limited, in that all of the rock excavated from a mine heading in a single drill and blast round is so jumbled and mixed that all of the rock must be removed from the mine, crushed, milled and processed for ore removal. Numerous mining operations involve the excavation of vein-type deposits, where the ore-bearing rock is restricted to a small section of the excavation face. A method whereby the ore-bearing rock could be selectively mined and transported to the surface for milling and extraction, with the remaining barren rock being left underground, would significantly improve the economics of many mining operations. For civil construction, the conventional drill and blast method is often limited, in that the large air blast and ground shock associated with each blast preclude the method being utilized in urban construction. Also the residual damage caused to the remaining rock often compromises the mechanical integrity of the structure, requiring additional and expensive ground support.